1. Field of the Invention
The present invention relates to a photographic lens having a Gauss orthoscopic lens having six lens elements which are contained in two lens groups.
2. Description of the Related Art
This type of photographic lens has been known in, for example, Japanese Laid-Open Patent Publications (No.48-25528 and No.58-9117). Both of these applications have a two-lens group arrangement. The front lens group contains first, second and third lens elements, all of which are positive meniscus lenses having convex surfaces facing the object side. The second and third lens elements are cemented. The rear lens group contains the fourth, fifth and sixth lens elements. The fourth lens element is either positive meniscus lens or negative meniscus lens having a convex surface facing the image side. The fifth lens element having two concave surfaces, and the sixth lens elements having two convex surfaces, are cemented.
However, in the above-mentioned photographic lenses of the related art, aberration fluctuations, which occur due to a change of magnification when focusing is carried out to comply with a change of the object distances, are relatively large. Consequently, coma increases more when focusing is carried out on the object at a closer distance than when focusing is carried out on the object at a longer object distance, and a change of field curvature becomes excessive. In other words, the closer the object distance is, the more coma increases. Quality of image-forming performance worsens considerably especially when close-up photography is carried out at a magnification of around 0.5.